This invention relates to the field of microwave cooking and more specifically to an improved method and apparatus for the control of cooking time in a microwave oven.
Cooking by means of microwave energy has become increasingly popular in recent years. One of the major attractions of microwave cooking has been its cooking speed. However, because microwave cooking times are generally shorter than cooking the same food by more conventional means, there is a tendency for some users to misjudge the proper cooking time. In order to alleviate this problem, manufacturers have attempted to develop sophisticated control schemes which will more or less automatically select the appropriate cooking time.
One such method is disclosed in U.S. Ser. No. 73,077 filed Sept. 6, 1979 by Ronald G. Buck and assigned to the assignee of the present application. That application discloses a method wherein the microwave power absorbed by the food over time is determined and compared to a predetermined and stored value of total power required for cooking to doneness. The total cooking time required is then determined. The power is continually monitored and the total cooking time is continually readjusted to compensate for variations in line power (voltage).
The above described method, while satisfactory, requires a large amount of empirically determined food cooking data reflecting various power levels. Relatively large memory storage is required and somewhat complex calculations of food cooking time versus power are required.
Ser. No. 167,304 filed July 10, 1980 by Ronald G. Buck et al discloses an apparatus for measuring the power delivered to the magnetron of a microwave oven and controlling the cooking time in response to delivered power. This technique involves measuring voltage and current on the primary side of the high voltage transformer and multiplying them in a four-quadrant multiplier to obtain a signal proportional to power. Converting the signal to digital form and comparing it with a factory calibration gives the necessary power information for the time control method described in the earlier mentioned Buck application.